Rocket propulsion method using hydrocarbon fuels containing aminoalkyl acrylate polymers



United States Patent ROCKET PROPULSION METHOD USING HYDRO- CARBON FUELS CONTAINING AMINOALKYL ACRYLATE POLYMERS Olaf E. Larsen, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Oct. 27, 1958, Ser. No. 769,952 Claims. (Cl. 6035.4)

This invention relates to rocket propellants. In one aspect, this invention relates to the addition of a small amount of a surface active agent to a liquid hydrocarbon fuel to enhance rocket motor performance characteristics when said fuel is used with a nitric acid oxidizer in a rocket motor.

Rocket motors are operated by burning a mixture of fuel and oxidant in a combustion chamber and causing the resulting gases to be expelled through a nozzle at high velocity. Liquid propellants are frequently preferred over solid propellants where it is necessary to vary thrust during flight. Liquid propellants can be classified as bipropellants and as monopropellants and the latter are either a single compound or mixtures of compounds. The principal elements of a rocket motor utilizing a liquid fuel comprise a combustion chamber, exhaust nozzle, an injection system, and propellant control valves. The propellent gases are produced in the combustion chamber at pressures governed by the chemical characteristics of the propellant, its rate of combustion, and the cross-sectional area of the nozzle throat. The gases are ejected into the atmosphere through the nozzle with supersonic velocity. The function of the nozzle is to convert the pressure of the propellent gases into kinetic energy. The reaction of the discharge of the propellent gases constitutes the thrust developed by the rocket motor.

The present invention relates to utilizing a liquid bipropellant system in a rocket motor. In the operation of rocket motors utilizing this system of propellants, it is usually desirable to inject the oxidizer component and the fuel component into the combustion chamber of the rocket motor as separate streams. If the fuel component is a hypergolic fuel, it is necessary that said fuel component and said oxidizer component be introduced as separate streams so that the initial contact occurs in the combustion chamber because spontaneous ignition occurs upon said initial contact. If, however, the fuel component is a non-hypergolic fuel, the oxidizer component and the fuel component can be mixed immediately prior to introduction into the combustion chamber and the introduced mixture, which is introduced as a single stream, can be ignited by any suitable ignition means, such as an electrical igniter.

A number of problems have been encountered in the development of liquid bipropellant rocket motors using hydrocarbon fuels and nitric acid oxidizers. Rapid and smooth ignition and stable combustion are two major problem areas related to the physical and chemical compositions of the reactants. Most hydrocarbons, and hydrocarbon blends such as the JP-type fuels, are non-hypergolic with nitric acid oxidizers and require an independent source of energy for ignition. Both low frequency and high frequency combustion oscillations in the combustion chamber, such as those referred to as chugging and screaming respectively, and which may result in unstable operation of the rocket motor, or even flame out, are forms of combustion instability that are effected by fuel type.

When a nitric acid oxidizer and a liquid hydrocarbon are mixed, certain precursor reactions take place with the evolution of considerable thermal energy during the imtial exothermic reactions which occur upon mixing. It has been found that a correlation exists between the amount of thermal energy released when a liquid hydrocarbon is ice mixed with a nitric acid oxidizer and the operation of the rocket motor when said fuel is burned therein. It has been found that the greater the amount of total thermal energy released, the more suitable the fuel is as a fuel for a rocket motor, i.e., more rapid and smooth ignition, and more stable combustion will occur in the combustion chamber of the rocket motor. The amount of thermal energy released upon mixing of a liquid hydrocarbon fuel and a nitric acid oxidizer can be determined by measuring the amount of temperature increase which occurs when said fuel is added to said oxidizer. It has been found that the rate-of-temperature rise is related to the ease of ignition of the fuel and oxidizer mixture and the over-all burning process, and the total amount of energy produced is related to the over-all combustion stability.

In accordance with the invention, it has been found that the reactions between a normally liquid hydrocarbon and a nitric acid oxidizer can be enhanced by incorporating a surface active agent in said normally liquid hydrocarbon. Enhancing the reaction between said liquid hydrocarbon and the nitric acid oxidizer also enhances the performance characteristics of the rocket motor wherein said bipropellant system is used. However, as discussed further hereinafter, all surface active agents are not effective to enhance the reaction between liquid hydrocarbons and nitric acid.

Thus, broadly speaking, the present invention resides in the use of a normally liquid hydrocarbon fuel having dissolved therein a copolymer of a predominantly non-polar alkyl acrylate monomer with an aminoalkyl acrylate monomer which contains a basic nitrogen atom, as the fuel component in a nitric acid-liquid hydrocarbon bipropellant system for developing thrust in a reaction motor, said copolymer being present in an amount suflicient to enhance the reaction between said nitric acid and said liquid hydrocarbon.

An object of this invention is to provide an improved liquid bipropellant system for use in rocket motors. Another object of this invention is to provide an improved method for the operation of rocket motors utilizing a liquid bipropellant system. Still another object of thls invention is to enhance the reaction between a normally liquid hydrocarbon fuel and a nitric acid oxidizer in a liquid bipropel-lant system. Other aspects, objects, and advantages of this invention will be apparent to those skilled in the art in view of this disclosure.

Thus, according to the invention, there is provided a method for developing thrust by the combustion of bipropellant components in a combustion chamber of a reaction motor, which method comprises: injecting a nitric acid oxidizer component containing at least about weight percent HNO and a normally liquid hydrocarbon fuel component into said combustion chamber; igniting and burning a mixture of said components in said combustion chamber to form products of combustion; and exhausting said products of combustion from said motor; said fuel component comprising from 99 to weight percent of a normally liquid hydrocarbon and from 1 to 5 weight percent of a copolymer formed by copolymerizing, in parts by weight per 100 parts of monomers, from 5 to 50 parts of at least one monomer selected from the group of alkyl acrylate esters having the formula with from 95 to 50 parts of at least one monomer selected from the group consisting of aminoalkyl acrylates having the formula wherein each R is selected from the group consisting of hydrogen, and alkyl radicals containing from 1 to 3 carbon atoms; each R is an alkyl radical containing from to 18 carbon atoms; each R is an alkylene radical containing from 1 to 8 carbon atoms; and each R is selected 5 from the group consisting of hydrogen, and alkyl radicals containing from 1 to 18 carbon atoms.

Suitable predominantly non-polar alkyl acrylate monomers for use in the practice of the invention include, among others, those given in Table I below:

TABLE I.ALKYL ACRYLATE MONOMERS Decyl methacrylate Dodecyl acrylate Dodecyl methacrylate Tetradecyl methacrylate Tridecyl methacrylate Hexadecyl methacrylate Octadecyl methacrylate Dodecyl ethacrylate Hexadecyl ethacrylate Dodecyl propacrylate Hexadecyl propacrylate Aminoalkyl acrylate monomers containing a basic nitrogen atom which are suitable for ues in the practice of the invention include, among others, those given in Table II below:

TABLE II.AMINOALKYL ACRYLATES Aminomethyl acrylate Aminomethyl methacrylate Aminopentyl metha crylate Aminopropyl methacrylate Aminopentyl acrylate Aminohexyl methacrylate Aminoheptyl methacrylate Aminooctyl methacrylate Aminomethyl ethacrylate Aminomethyl propacrylate Aminohexyl ethacrylate Aminooctyl ethacrylate Amino-Z-ethylhexyl acrylate Dimethylaminomethyl methacrylate Diethylarninoethyl acrylate Diisopropylaminoethyl methacrylate Dihexylaminoethyl methacrylate Di- 2,4,6-triethyloctyl) aminoethyl methacrylate Didodecylaminoethyl methacrylate Dioctadecylaminoethyl methacrylate Dimethylaminopropyl methacrylate Dimethylarninobutyl acrylate Dimethylaminopentyl methacrylate Dimethylaminooctyl methacrylate Dihexylaminooctyl methacrylate Dihexylaminooctyl ethacrylate Dioctylaminooctyl methacrylate Dimethylamino-(2-ethylpropyl) acrylate The above-mentioned acrylate monomers can be copolymerized by any method known to those skilled in the art to form the copolymers used in the practice of the invention. Normally these copolymers are prepared by emulsion, bulk, and solution polymerization processes. For example, said monomers can be emulsified in water and a polymerization catalyst such as benzoyl peroxide added thereto. The polymerization can be effected at temperature in the range of 20 to 160 C. until the desired degree of polymerization has been eifected. The resulting copolymer can be recovered from the reaction mixture after coagulation thereof with sodium chloride. Further 70 information regarding the details of said copolymerization can be found in US. Patents 2,138,031 and 2,138,763, issued to George D. Graves on November 29, 1 938. Said monomers are preferably copolymerized in amounts, in parts by weight per 100 parts of monomers, ranging from 5 to parts of at least one of said alkyl acrylate monomers with from 95 to 50 parts of at least one of said amino alkyl acrylate monomers.

Suitable copolymers prepared from the above described monomers and which are suitable for use in the practice of the invention include among others the following:

TAB LE III Monomer Ratio Copolymers Decyl methacrylate/aminopentyl methacrylate,

Dodecyl methacrylate/aminopentyl acrylate.

Tet-radecyl methaerylate/aminooctyl methacrylate.

Tridecyl met-hacrylate/aminoethyl ethacrylate.

Dodecyl ethacrylate/amino-2-ethylhexyl acrylate.

Hexadecyl ethacrylate/dioctarleeylaminoethyl crylate.

Hexadecyl ethacrylate/dioctadecylaminoethyl mothacry te.

Dodecyl propacrylate/dimethylaimnopropyl methaerylate.

Hexadeoyl propacrylate/dimethylaminooctyl methacrylate.

Decyl methacrylate/dihexylaminooctyl methacrylate.

Dodecyl methacrylate/dimet-hylamiuo-(2-ethylpropyl) acrylate.

Dodecyl acrylate/aminoethyl acrylate.

Hexadecyl methacrylate/aminoethyl methacrylatc.

Octadecyl ethaerylate/didodecyl aminoethyl ethacrylate.

Dodecyl methacrylate/diethylarmnoethyl methaerylate.

Dodecyl methacrylate/diethylaminoethyl methacrylate.

' on said hydrocarbons. However, in some instances larger and smaller amounts can be effectively used.

In the bipropellants used in the practice of the invention, the ratio of the liquid hydrocarbon fuel component to the nitric acid oxidizer component is preferably near stoichiometric. Said ratio can be in the range of 0.75 to 1.25 times that of the stoichiometric amount. The stoichiometric amount of oxidizer is defined as the amount required to obtain complete combustion to nitrogen, carbon dioxide, and water. In computing said stoichiometric amount of oxidizer, consideration is given to the amount of surface active agent which is dissolved in the normally liquid hydrocarbon. Thus, the stoichiometric amount of oxidizer includes the amount necessary to oxidize said surface active agents as well as the amount necessary to oxidize the normally liquid hydrocarbon with which the nitric acid is mixed in the combustion chamber of the reaction motor. A slightly fuel-rich mixture is usually required to give an optimum rocket motor performance.

Since water tends to retard combustion of the acid with the liquid hydrocarbon fuel, the nitric acid used in a propellant system is preferably substantially free of water. Thus, the presently most preferred oxidizer is anhydrous nitric acid. However, other more dilute nitric acids can be used in the practice of the invention. White fuming nitric acids and red fuming nitric acids of varying concentrations are available commercially, and all are useful in the practice of this invention. White fuming nitric acid usually contains about 90 to 99 weight percent HNO from 0 to 2 weight percent N0 and up to about 10 weight percent water. Red fuming nitric acid usually contains about to weight percent HNO from 2 to 25 weight percent N0 and up to about 10 weight percent water. Of course, mixtures of the above-described acids can be employed to give an acid having any intermediate composition, and all are useful as oxidizers in the practice of this invention. Thus, it has been found that nitric acids of all types containing at least about 70 weight percent HNO are useful as oxidizers in the practice of this invention.

The following examples will serve to further illustrate the invention:

Example I A number of runs were made in which two volumes of red fuming nitric acid were placed into an enclosed mixing chamber equipped with a stirrer which extended into said acid. A thermocouple, connected through an amplifier to a temperature recorder, also extended into said acid. After said acid had been placed in the mixing chamber, the amplifier and recorder were turned on and the stirrer was started. One volume of a JP-4 hydrocarbon jet fuel having 3 weight percent of the candidate surface active agent dissolved therein was then added to said acid. The total increase in temperature of the resulting mixture in said mixing chamber in minutes of reaction time was recorded.

The red fuming nitric acid employed in these tests contained 77 weight percent HNO 21 weight percent N and 2 weight percent water. The JP-4 liquid hydrocarbon jet fuel used in these tests had the physical properties listed in Table V given below. The results of the above described runs are given in Table IV below and are there compared with a control run wherein the hydrocarbon fuel contained no surface active agent.

TABLE IV.MIXING OF ACID AND JP-4 FUEL [Effect of additives in .TP-4 fuel on thermal energy released] Condensation product of nonyl phenol with four moles ethylene oxide.

l-hydroxyethyLLheptadecenyl glyoxaldine (the specific difference between Amine O and Amine 220 is not presently available).

0A sulfated ester, anionic type surfactant, 65 percent aqueous solution.

Defined as a fatty amide in Sistay and Woods Encyclopedia of Surface Active Agents.

N-alkyl-trimethylenediamine.

Polyoxyethylene sorbitan trioleate.

The above results show conslusively that not all surface active agents are suitable for enhancing the reaction between a liquid hydrocarbon fuel and a nitric acid oxidizer. It should be noted that: in Runs 2, 3 and 5 the results were actually worse than in Control Run 1; in Runs 4, 6, 7, and 8 the results obtained were the same as or only slightly better than in Control Run 1; whereas in Run 9, employing one of the copolymer additives of the invention, the results obtained were outstanding superior to Control Run 1. p

Table V given below gives properties of a typical JP-4 jet fuel.

TABLE V.A TYPICAL ZIP-4 JET FUEL 6 Existent gum, mg./ 100 ml. 1.7 Potential gum, mg./ 100 ml 1.8 Freezing point, F. -70 Reid vapor press, p.s.i 1.8 Density, gr./cc. at 20 C. 0.7720 Sulfur, total, wt. percent 0.109 L. heat of comb., B.t.u./lb 18,651 Aniline point, F. 128.5 Aromatics, vol. percent 13.2 Bromine No. 1.1 Smoke point, mm. 24.5 Smoke volatility index 56.8

1 Est.

While the JP-4 jet fuel described in Table V above is one of the presently preferred liquid hydrocarbon fuels for use in the practice of the invention, it is to be understood that other normally liquid hydrocarbon fuels can be so used. Thus, other hydrocarbon jet fuels can also be used. Suitable normally liquid hydrocarbons which can be used in the practice of the invention include paraffin, cycloparaffin, and aromatic hydrocarbons in the C-5 t-o C-30 range or mixtures thereof. Examples of such hydrocarbon fuels are normal pentane, normal hexane, normal heptane, benzene, kerosene, isooctane, 2,3- dimethylbutane, diisobutylene, cyclohexene, cyclohexane, isodecane, methylcyclohexane, toluene, hexadacane, eicosane, hexacosane, pentatricontane, gasoline, naphthas, and the like. Hydrocarbons in the C-5 to C1'6 range are preferred.

Since variations and modifications of the invention can be made by those skilled in the art without departing from the scope or spirit of said invention, it is to be understood that all matter herein set forth in the above discussion is merely illustrative and does not unduly limit the invention.

I claim:

1. A method for developing thrust by the combusion of bipropellant components in a combustion chamber of a reaction motor, which method comprises: injecting a nitric acid oxidizer component containing at least about 70 weight percent I-INO}, and a normally liquid hydrocarbon fuel component into said combustion chamber; igniting and burning a mixture of said components in said combustion chamber to form products of combustion; and exhausting said products of combustion from said motor; said fuel component comprising from 99 to weight percent of a normally liquid hydrocarbon and from 1 to 5 weight percent of a copolymer formed by copolymerizing, in parts by weight per 1 00 parts of monomers, from 5 to 50 parts of at least one monomer selected from the group of alkyl acrylate esters having the formula:

with from 95 to 50 parts of at least one monomer selected from the group consisting of aminoalykl acrylates having the formula:

wherein: each R is selected from the group consisting of hydrogen, and alkyl radicals containing from 1 to 3 carbon atoms; each R is an alkyl radical containing from 10 to 18 carbon atoms; each R is an alkylene radical containing from *1 to 8 carbon atoms; and each R is selected from the group consisting of hydrogen, and alkyl radicals containing from 1 to 18 carbon atoms.

2. The method of claim 1 wherein the ratio of said oxidizer component to said fuel component is within the range of 0.75 to 1.25 times the stoichiometric ratio.

7 8 3. The method of claim 1 wherein said oopolymer is 10. The method of claim 1 wherein said copolymer is 90:10 dodecyl acrylate/aminoethyl acrylate. 95:5 dedecyl ethacrylate/amino2-ethy1hexyl acrylate.

4. The method of claim 1 wherein said copolymer is 50:50 hexadecyl methacrylate/aminoethyl methacrylate. References Cited y the Examine! 5. The method of claim 1 wherein said copolymer is UNITED STATES PATENTS 95.5 octadecyl ethacrylate/didodecyl amlnoethyl ethacrylate 2,461,797 2/1949 ZWicky 60-35.4 2 573 471 10/1951 Malina et a1. 6035.4

6. The method of claim 1 wherein said copolymer is 90:10 dodecyl methacrylate/diethylaminoethyl meth- 2604453 7/1952 Popkm 44 62 2,697,656 12/1954 Stayner.

acrylate 10 2,697,657 12/1954 Stayner.

7. The method of claim 1 wherein said copolymer is 80:20 dodecyl methacrylate/diethylaminoethyl meth- FOREIGN PATENTS acrylate.

8. The method of claim 1 wherein said copolymer is 734632 8/1955 Great Britain 55:45 decyl methacrylate/aminopentyl methacrylate. 15 I 9. The method of claim 1 wherein said copolymer is CARL QUARFORTH Puma), Examiner 75 :25 dodecyl methacrylate/aminopentyl acrylate. LEON D. ROSDOL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0 F CRRECTION Patent No. 3,230,700 January 25, 1966 Olaf E0 Larsen It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 57, for "combusion" read combustion column 7, llne 6, for "9505" read M 95:5 column 8, line 2,

for "dedecyl" read dodecyl M Signed and sealed this 28th day of June 19660 Attest:

ERNEST W. SWLDER EDWARD J. BRENNER At testing Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 230, 700 January 25, 1966 Olaf E0 Larsen It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 37, for "combusion" read combustion column 7, line 6, for "950 5" read 95 :5 column 8, line 2, for "dedecyl" read dodecyl Signed and sealed this 28th day of June 19660 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesling Officer Commissioner of Patents 

1. A METHOD FOR DEVELOPING THRUST BY THE COMBUSTION OF BIPROPELLANT COMPONENTS IN A COMBUSION CHAMBER OF A REACTION MOTOR, WHICH METHOD COMPRISES: INJECTING A NITRIC ACID OXIDIZER COMPONENT CONTAINING AT LEAST ABOUT 70 WEIGHT PERCENT HNO3 AND A NORMALLY LIQUID HYDROCARBON FUEL COMPONENT INTO SAID COMBUSTION CHAMBER; IGNITING AND BURNING A MIXTURE OF SAID COMPONENTS IN SAID COMBUSTION CHAMBER TO FORM PRODUCTS OF COMBUSTION; AND EXHAUSTING SAID PRODUCTS OF COMBUSTION FROM SAID MOTOR; SAID FUEL COMPONENT COMPRISING FROM 99 TO 95 WEIGHT PERCENT OF A NORMALLY LIQUID HYDROCARBON AND FROM 1 TO 5 WEIGHT PERCENT OF A COPOLYMER FORMED BY COPOLYMERIZING, IN PARTS BY WEIGHT PER 100 PARTS OF MONOMERS, FROM 5 TO 50 PARTS OF AT LEAST ONE MONOMER SELECTED FROM THE GROUP OF ALKYL ACRYLATE ESTERS HAVING THE FORMULA: 